Nonradical-dominated peroxymonosulfate activation through bimetallic Fe/Mn-loaded hydroxyl-rich biochar for efficient degradation of tetracycline

Biochar-based transition metal catalysts have been identified as excellent peroxymonosulfate(PMS)activators for producing radicals used to degrade organic pollutants.However,the radical-dominated pathways for PMS activation severely limit their practical applications in the degradation of organic pollutants from wastewater due to side reactions between radicals and the coexisting anions.Herein,bimetallic Fe/Mn-loaded hydroxyl-rich biochar(FeMn-OH-BC)is synthesized to activate PMS through nonradical-dominated pathways.The as-prepared FeMn-OH-BC exhibits excellent catalytic activity for degrading tetracycline at broad pH conditions ranging from 5 to 9,and about 85.0%of tetracycline is removed in 40 min.Experiments on studying the influences of various anions(HCO_(3)^(−),NO_(3)^(−),and H_(2)PO_(4)^(−))show that the inhibiting effect is negligible,suggesting that the FeMn-OHBC based PMS activation is dominated by nonradical pathways.Electron paramagnetic resonance measurements and quenching tests provide direct evidence to confirm that 1O2 is the major reactive oxygen species generated from FeMn-OH-BC based PMS activation.Theoretical calculations further reveal that the FeMn-OH sites in FeMn-OH-BC are dominant active sites for PMS activation,which have higher adsorption energy and stronger oxidative activity towards PMS than OH-BC sites.This work provides a new route for driving PMS activation by biochar-based transition metal catalysts through nonradical pathways.

Coupling of sulfur and boron in carbonaceous material to strengthen persulfate activation for antibiotic degradation:Active sites,mechanism,and toxicity assessment

Carbon-mediated persulfate advanced oxidation processes(PS-AOPs)are appealing in contaminant remediation.For the first time,S,B-co-doped carbon-based persulfate activators were synthesized through direct carbonization of sodium lignosulfonate and boric acid.By degrading sulfamethoxazole(SMX),CSB-750 obtained 98.7%removal and 81.4%mineralization within 30 min.In comparison with solo S or B doping,S and B co-doped carbon showed the coupling effect for enhanced catalysis.The rate constant(kobs)of 0.1679 min^(-1)was 22.38-and 279.83-fold higher than those of CS-750(0.0075 min^(-1))and CB-750(0.0006 min^(-1)),respectively.The degradation was efficient at strong acidic and weak basic conditions(pH 3-9).Substantial inhibition effect was presented at strong basic condition(pH 10.95)and in presence of CO_(3)^(2-).The CO_(3)^(2-)-caused inhibition was the combined result of the cooperation of pH and quenching O_(2)^(·-).Thiophene sulfur,BC_(3),BC_(2)O,and structural defects were identified as the active sites for PS activation.Radical and nonradical pathways were both involved in the CSB-750/PS/SMX system,where^(1)O_(2)dominated the degradation,SO_(4)^(·-),·OH and direct electron transfer played the subordinate role,and O_(2)^(·-)served as a precursor for the formation of partial^(1)O_(2).The toxicity of degradation system,the effect of real water matrix,and the reusability of carbocatalysts were comprehensively analyzed.Nine possible degradation pathways were proposed.This work focuses on the catalytic performance improvement through the coupling effect of S,B co-doping,and develops an advanced heteroatom doping system to fabricate carbonaceous persulfate activators.